1. Field of the Invention
The present invention relates to a photosensitive member for electrophotography, more particularly, relates to the photosensitive member for electrophotography which can be adopted for a copying machine for a digital image.
2. Description of the Related Art
In the photosensitive member which has formerly been employed in the field of the electrophotography, it is a general technical matter to form a surface protective layer on a photosensitive layer formed on an electroconductive support in order to prevent an abrasion of the photosensitive layer caused by a cleaning member and the like as well as an injection of charge into the photosensitive layer. It has been known that silica is a preferred compound for the surface protective layer from the viewpoint of a durability, said silica being constituted by three-dimensional network of siloxane bond (Si--O--Si bond). However, in the case of the surface protective layer consisting of only silica, there are problems that cracks occur on the surface of said layer, and an adhesion to the photosensitive layer becomes worse, and an electrostatic property of the photosensitive layer is lowered [see, for example, Japanese Patent Publication (KOKAI) Nos. 51155/1986].
For this reason, the surface protective layers have been proposed which are prepared by coating a solution comprising a mixture of polymers, such as acrylic resin, urethane elastomer, polyamide or the like and an organosilane which is a raw material of silica (solution for protection the surface) on the photosensitive layer and then curing said mixture [see, for example, Japanese Patent Publication (KOKAI) Nos. 141365/1991, 263660/1989, 341551/1993 and 135577/1991, and U.S. Pat. No. 5,260,157].
However, although the adhesion between the surface protective layer and the photosensitive layer is increased, there are various problems that a sensitivity is worse, an electric potential increases at the time of plate wearing, and harmful influences such as a fog and the like are brought about on the image quality. Although it has been proposed that an electroconductive metallic oxide is added to the surface protective layer in order to suppress the increase of the electric potential, harmful influences such as an image flowing, an image shading and the like are brought about at the time of plate wearing under the hot and humid circumstance.